A focal plane shutter subjects a film to a slit exposure. Therefore, a focal plane shutter is disadvantageous in the case where it is necessary to photograph clearly an object moving at high speed or in the case where synchronous photographing is effected with an electronic flash whose light emission duration is very short.
In order to overcome the difficulties, a variety of methods have been proposed in which an interchangeable lens with a lens shutter (hereinafter referred to merely as a "a lens") is combined with a focal plane single lens reflex camera (hereinafter referred to merely as "a camera"). In such system, when the focal plane shutter is fully opened, the lens shutter is operated.